The reason I passed on the Nano is to me a big deal and if I am wrong someone please correct me and tell me a way I am not seeing.
It's never a bad plan to be prepared for as many contingencies as possible. But you must always balance the tactical
with the practical
Whether a pistol has a slide release or not is so far down on my list of priorities in a pistol that it has absolutely no bearing (for me) as to whether or not I purchase a pistol that does or does not have one.
Everyone is different of course, but I do not use the slide stop in any way other than for convenience in releasing the slide with an empty magazine.
As for the scenario that you pose, first, I typically do not carry an extra magazine in the first place when carrying a pocket or sub-compact pistol. Round count is not my concern with this gun. If I felt the need for an extra magazine I would go up in size slightly to a compact or mid-size pistol that had more than double the capacity of two 6 round mags.
Second, I have no trouble whatsoever releasing an open slide with one hand on a loaded magazine without the use of a slide release.
Any hard edge with a 2" clearance will do. Nothing around that fits the bill? Your shoe will work fine! Barefoot on the beach? You got me there. Better have two mags and a pistol with a slide release